1. Field of the Invention
The present invention relates generally to hermetically sealed optical fiber arrays and methods for forming them. More specifically, the present invention relates to hermetically sealed optical fiber arrays used in optical sensor probes, and methods of making the optical fiber arrays using fluxless soldering techniques.
2. Description of Related Art
Optical sensor probes often require optical fiber arrays that must be sealed or protected from severe environments in which they may operate. The presently used methods for providing protection or isolating the optical fiber arrays involve non-hermetically bonding the optical fibers within the arrays to each other and to metal sleeves or V-groove structures.
Typically, sealed optical fiber arrays consist of bundles of metal-coated or uncoated optical fibers which are bonded together using a variety of techniques. In the case of uncoated optical fibers, the bonding techniques involve performing two different bonding steps. First, a bundle of optical fibers is formed consisting of individual uncoated optical fibers. The uncoated optical fibers are fused together to form a glass-to-glass seal between the individual uncoated optical fibers. Then the bundle of optical fibers is bonded inside a metal sleeve or V-groove structure using an organic adhesive, such as an epoxy.
There are significant problems associated with the organic adhesives utilized to bond the bundle of optical fibers to the sleeve. The performance of the optical fiber arrays is limited by the nature of the adhesive which can absorb or transmit moisture into moisture sensitive areas. Such adhesives will outgas organic material which will compromise the adhesive bond and contaminate sensitive areas. In environments with elevated temperatures, or in environments with strong oxidizers such as liquid oxygen, organic adhesives degrade, causing adhesive bond failures.
In the case where the optical fiber arrays are fabricated with metal-coated optical fibers, the optical fibers are soldered to each other and to a metal sleeve or metal support structure. Conventional soldering techniques are utilized to facilitate the soldering procedure. These methods comprise using a soldering iron and solder with flux.
This conventional method presents significant disadvantages attributed to the flux used during the soldering procedure. The flux is free to migrate, leaving voids within the soldered area. This mechanically weakens the solder bond and allows small molecules to diffuse into the soldered area. Additionally, flux soldering techniques do not facilitate control of the length of the solder bond along the sleeve or the supporting structure.
Accordingly, there is presently a need to provide hermetically sealed optical fiber arrays. There is also a need to provide methods for fabricating hermetically sealed optical fiber arrays.
There is a further need to provide hermetically sealed optical fiber arrays in which the optical fibers are bonded together and to a sleeve or supporting structure in such a manner as to avoid outgasing from the bond.
There is additionally a need to provide hermetically sealed optical fiber arrays in which the optical fibers are bonded together and to a sleeve or supporting structure in such a manner as to avoid degradation of the adhesive bond.